in tetrahydrofuran (N2); std. Schlenk technique; soln. of Na compd. (2 equiv.) in THF was slowly added to stirred suspn. of Zr compd. in THF at -78°C; warmed to room temp.; refluxed for 18 h; cooled; filtered; dried (vac.); sublimed (180°C, 0.1 Torr); elem.anal.;